Plants use two cAMP pathways to combat stress.

Researchers from the Institute of Science and Technology Austria (ISTA) and institutions in Germany, Saudi Arabia, the Czech Republic, and the United States have demonstrated that plants use two forms of the cAMP molecule in parallel signaling systems. Their work indicates that 2',3'-cAMP and 3',5'-cAMP have distinct enzymatic origins and produce different cellular responses. Arabidopsis thalianaThe authors point to the potential impact on studies of crop productivity and resilience under climate change.

cAMP, or cyclic adenosine monophosphate, acts as a second messenger in animals and plants. In mammals, the 3',5'-cAMP form has been more thoroughly characterized. In plants, the role of the molecule still had gaps. The new study expands this scenario by showing the presence and function of two structural isomers, with the same chemical formula but different atomic bonds.

The team analyzed seedlings of Arabidopsis thaliana by high-performance liquid chromatography coupled to mass spectrometry. The results indicated the endogenous presence of both forms. 2',3'-cAMP appeared at levels much higher than 3',5'-cAMP. The ISTA press release reports levels more than 60 times higher for 2',3'-cAMP compared to 3',5'-cAMP.

Production routes

Enzymatic assays also separated the production pathways. The plant adenylate cyclases AFB5 and HpAC1 produced 3',5'-cAMP from ATP. The TIR domain of the L7 protein, however, formed 2',3'-cAMP from RNA. The study also recorded dual activity in L7, with the ability to catalyze 3',5'-cAMP from ATP as well, a point interpreted by the authors as possible functional or evolutionary flexibility.

Multiomics analysis showed distinct responses in the metabolome, proteome, and transcriptome. 2',3'-cAMP activated a broad reprogramming of gene expression associated with stress adaptation. 3',5'-cAMP adjusted responses linked to nutritional status and cellular homeostasis. According to the article, the two isomers form dual signaling systems with specialized and partially overlapping functions.

In the transcriptome, 2',3'-cAMP induced a broader and faster response. After 30 minutes, treatment with Br-2',3'-cAMP resulted in 1.925 genes being upregulated and 1.958 genes being downregulated. After 6 hours, these numbers rose to 2.937 and 2.630 genes, respectively. Br-3',5'-cAMP led to 1.249 genes being upregulated and 1.312 being downregulated in 30 minutes. After 6 hours, the numbers reached 2.690 and 2.429.

Stress-related processes

Genes induced by 2',3'-cAMP showed enrichment in stress-related processes. The study cites responses to hypoxia, reactive oxygen species, injury, water deficit, salinity, and bacterial infection. Genes induced by 3',5'-cAMP, on the other hand, had a more restricted association with zinc deprivation, cell wall modification, and cellular response to oxygen levels.

In the proteome, 2',3'-cAMP also caused broader changes. The authors observed greater alterations in proteins linked to stress pathways and specialized metabolism. 3',5'-cAMP primarily affected primary metabolic processes related to growth and maintenance.

Developmental data indicated dose- and plant-stage dependent effects. Germination did not change at the tested concentrations. In 7-day-old seedlings, 2',3'-cAMP increased primary root length at concentrations of 10 and 100 μM. 3',5'-cAMP promoted root elongation only at 100 μM. In 15-day-old seedlings, 3',5'-cAMP increased cotyledon and true leaf area, mainly at 100 μM.

Proposed hypothesis

The authors propose that maintaining two parallel and connected pathways allows for fine-tuning of cellular regulation. Each isomer would control specific parts of metabolism, gene expression, and stress responses. The interaction between the pathways can also generate redundancy and specialization, which would enhance the robustness of plant responses to environmental stimuli.

The study also points to methodological limitations. The researchers used brominated analogs to track metabolism and biological effects. These compounds mimic natural molecules, but may differ in cellular absorption, metabolic stability, or binding affinity. The authors advocate for future genetic studies to manipulate endogenous cyclase activities and validate the pharmacological findings.

The research establishes a basis for investigating how plants combine growth, defense, and environmental adaptation through cyclical signaling. According to the authors, understanding these pathways can guide future strategies to increase resilience and agricultural productivity under varying environmental conditions.

Further information can be found at science.org/doi/10.1126/sciadv.aea7828